1. Field of the Invention
The present invention relates to a layered structure that has a FePt system magnetic layer (hereinafter as FePt magnetic layer). Particularly, the present invention relates to a layered structure that is able to decrease an ordered temperature for a FePt alloy equal to or below 300° C., and to realize a high coercive force. The layered structure that has the FePt magnetic layer according to the present invention is used, for example, as a hard magnet for a bias magnetic field application of a magnetoresistive effect (MR) element, a microwave assist recording oscillation element, and a next generation magnetic recording medium.
2. Description of the Related Art
An L10 structural FePt ordered alloy with a high uniaxial crystalline magnetic anisotropy is noted as a next generation ultra high density magnetic recording medium material because the alloy includes a minute nano-size particle maintains ferromagnetic characteristics.
The FePt ordered alloy is also expected to be used as a magnet because it has a high uniaxial crystalline magnetic anisotropy. A FePt also has merits in that it is superior in corrosion resistance and resistance to oxidation compared to rare earth metals, such as Nd and Sm.
The L10 structural FePt ordered alloy is stable in view of thermodynamics at room temperature. However, a FePt layer, which is formed by a sputtering method, cannot be transformed (crystal-ordered) into the ordered structure because it does not pass through the ordered-random transformation point that exists at a high temperature during the forming layer process. Therefore, in order to obtain the L10 ordered structure, it is necessary to conduct the following high temperature processes, typically, at over 500° C.; forming a layer on a heated base, or annealing a random alloy thin layer after layer formation.
However, structural materials used, for example, as a hard disk device with a thin film magnetic head, have a temperature tolerance only up to about 300° C., and do not have a tolerance for high temperature processes over 500° C. Therefore, it is expected to provide a layered structure with a FePt magnetic layer that has an L10 structural FePt ordered alloy formed equal to or below 300° C.
Related art that especially relates to a layered structure of the present invention is Japanese laid-open patent publication number JP2003-313659. This related art discloses that a seed layer, a base layer, and an L10 ordered alloy are formed in this order on a supporting substrate. This related art also describes that the ordered temperature is controlled by residual oxygen concentration regardless of base materials; therefore, its specific structure and operation are different from that of the present invention.
The present invention is provided under these actual circumstances. The object of the present invention is to provide a layered structure with a FePt magnetic layer that has an L10 structural FePt ordered alloy formed equal to or below 300° C.